This meter uses optical detection for when plugs are inserted into the current jacks. The components in question are part the photo-transistor detector circuit for the mA jack directly on the other side of the board.
Maybe the jack has some crud in it that causes the lead alarm to go off, and the previous owner removed the components to silence it. Just a guess, as I've done exactly this to a 27-II model with jacks that were damaged by solvent.
The transistor "1AM" is a MMBT3904 general-purpose NPN transistor. The "104" resistor is 100K. I cannot get an in-circuit read on the cap, as I found a voltage differential on it due to the super-cap. Probably just a filter to prevent false triggering due to ambient IR?